Paper is made by forming a mat of fibers, normally wood fibers, on a moving wire screen. The fibers are in a dilution with water constituting usually above 95 percent of the mix. As the paper web leaves the forming screen, it may be still over eighty percent water. The paper web travels from the forming or wet end of the papermaking machine and enters a pressing section where, with the web supported on a felt, the moisture content of the paper is reduced by pressing the web to a fiber content of about forty-two percent. After the pressing section, the paper web is dried on a large number of steam heated dryer rolls, so the moisture content of the paper is reduced to about five percent.
One type of dryer is the apparatus manufactured by Beloit Corporation of Beloit, Wis. and sold under the trade name "Bel-Champ." The Bel-Champ dryer has a single tier of dryer upper rolls with vacuum reversing rolls disposed therebetween. As the web, supported by a felt, progresses through a single dryer section, typically composed of five or more dryer rolls, the same face of the web is repeatedly placed in contact with the heated dryer roll surfaces. To effectively dry both faces of the web, the first felt is directed away from the web and a second felt is brought into contact with the opposite face. Once supported on the second felt the web is led through a succeeding dryer section where the alternate face is placed in contact with the heated dryer rolls. The transfer of the web between dryer sections takes place in a fully supported draw between two vacuum rolls. Each felt extends from a vacuum roll to a felt roll which is spaced either above or below the vacuum rolls.
On occasion it becomes necessary to separate the felts on the order of one half inch. In the past this separation has been achieved by using air or hydraulic cylinders to move the felt rolls horizontally. However, in order to retain the felts on the rollers as they are moved, it is essential that the roll be advanced evenly. As a felt is typically wrapped in the range of 90 degrees around the felt roll, angling of the roll in motion may cause the felt to run off the machine. Even movement is effectively obtained by employing a large cross-shaft. Such shafts, however, are costly.
Furthermore, because the felt rolls must be spaced several feet from the vacuum rolls, the felt roll must be moved up to ten inches or more in order to achieve the desired separation of the felts of about one half inch. Additionally, this significant displacement of the felt rolls changes the lengths of the felt runs, requiring a stretcher assembly to take up the additional felt length. In order to accommodate the stretcher, the felt rolls must be moved slowly to insure that the stretcher has enough time to respond and maintain felt tension. As the felt rolls are spaced above and below the web, the separation operation is also difficult to observe.
What is needed is an economical mechanism for separating the felts in a dryer section break which is rapid and effective.